Conventionally, positioners have been used in controlling the driving of valves and in controlling the driving of process automation and other common industrial equipment, enabling the control of the degree of opening of a valve through attaching the positioner to the valve.
FIG. 3 illustrates the structure of the critical portions of a positioner that enables the control of the degree of opening of a valve. In this diagram, 100 is a positioner, where this positioner 100 is structured from an electro-pneumatic converting portion 101 for converting to a pneumatic signal Pn a valve opening signal that is sent in an electric signal from a higher-level controller 200, and a pilot relay (pressure signal amplifying device) 102 for amplifying the air pressure signal (input air pressure) Pn, converted by this electro-pneumatic converting portion 101, and outputting it to a valve 300 as an output air pressure signal (output air pressure) Po.
The pilot relay 102 used in such a positioner 100 may be of the single-action type, wherein a single output air pressure Po is outputted for a single input air pressure Pn, or a double-action type, wherein two output air pressures Po1 and Po2 are outputted in relation to a single input air pressure Pn. The double-action pilot relay 102 has two output ports, where the output air pressure Po1 of the first output port is higher than the output air pressure Po2 of the second output port when the valve 300 is operated in the forward direction, and the output air pressure Po2 of the second port is higher than the output air pressure Po1 of the first port when operated in the reverse direction.
FIG. 4 illustrates a structure of the double-action pilot relay disclosed in Japanese Unexamined Patent Application Publication 2005-282718 (“JP '718”). In this figure, 401 is a housing, where an input air pressure chamber 402, a first supply air pressure chamber 403, a second supply air pressure chamber 404, a first output air pressure chamber 405, a second output air pressure chamber 406, a discharge air chamber 407, and a bias chamber 408 are provided within the housing 401.
Moreover, a diaphragm 409 that is displaced by the input air pressure (the nozzle back pressure) Pn that is directed into the input air pressure chamber 402 is provided within the housing 401, where a spool (a movable body) 410 is provided on the diaphragm 409 so as to be able to move in the direction of the arrow A and the direction of the arrow B. The spool 410 has a first opening 410a that is located at the first output air pressure chamber 405, a second opening 410b that is located at the second output air pressure chamber 406, and a discharge air duct 410c for connecting the first opening 410a and the second opening 410b to the discharge air chamber 407.
A ring wall 411 is formed as a valve seat within the housing between the first supply air pressure chamber 403 and the first output air pressure chamber 405. This ring wall 411 fulfills the role as a first dividing wall for partitioning between the first supply air pressure chamber 403 and the first output air pressure chamber 405. A ring wall 412 is formed within the housing between the second supply air pressure chamber 404 and the second output air pressure chamber 406. This ring wall 412, as a valve seat fulfills the role as a second dividing wall for partitioning between the second supply air pressure chamber 404 and the second output air pressure chamber 406.
Moreover, a first poppet valve 413 is provided so as to be able to slide to the left and right through a center hole 411a in the ring wall 411, between the first supply air pressure chamber 403 and the first output air pressure chamber 405. The first poppet valve 413 has, integrally, a discharge air valve 413a for opening and closing the first opening 410a of the spool 410, and a supply air valve 413b for opening and closing the center hole (a first connecting hole) 411a in the ring wall 411.
A second poppet valve 414 is provided so as to be able to slide to the left and right through a center hole 412a in the ring wall 412, between the second supply air pressure chamber 404 and the second output air pressure chamber 406. The second poppet valve 414 has, integrally, a discharge air valve 414a for opening and closing the second opening 410b of the spool 410, and a supply air valve 414b for opening and closing the center hole (a second connecting hole) 412a in the ring wall 412.
Moreover, the first supply air pressure chamber 403 is provided with a first spring 415 for biasing the first poppet valve 413 in the direction of the arrow B, that is, in the direction wherein the supply air valve 413b closes the first connecting hole 411a. The second supply air pressure chamber 404 is provided with a second spring 416 for biasing the second poppet valve 414 in the direction of the arrow A, that is, in the direction wherein the supply air valve 414b closes the second connecting hole 412a. 
In this double-action pilot relay, the supply air pressure Ps is supplied through the air supplying pipe 417 to the first supply air pressure chamber 403 and the second supply air pressure chamber 404, and the input air pressure Pn is guided through the nozzle back pressure injecting pipe 418 into the input air pressure chamber 402. Moreover, the output air pressure Po1 is outputted to the valve 300 through the first air outputting pipe 419 from the first output air pressure chamber 405 and the output air pressure Pot is outputted to the valve 300 through the second air outputting pipe 420 from the second output air pressure chamber 406. Note that a bias chamber 408 is formed between the diaphragms 409 and 421, support on the spool 410, where a supply air pressure Ps is supplied through the air supplying pipe 417 to this bias chamber 408. Additionally, the discharge air chamber 407 is connected to atmosphere.
In this double-action pilot relay, when the input air pressure Pn is decreased, the diaphragm 409 moves to the side of the arrow A, and, concomitantly, the spool 410 that is supported on the diaphragm 409 moves to the side of the arrow A. At this time, the spool 410, through this movement, presses the first poppet valve 413 downward against the biasing force of the first spring 415, and, as a result, the supply air valve 413b of the first poppet valve 413 opens the first connecting hole 411b. At this time, the first opening 410a of the spool 410 is closed by the discharge air valve 413a of the first poppet valve 413. On the other hand, the second poppet valve 414 is pushed upward by the biasing force of the second spring 416, and, accordingly, the supply air valve 414b of the second poppet valve 414 closes the second connecting hole 412b. At this time, the second opening 410b of the spool 410 is opened by the discharge air valve 414a of the second poppet valve 414.
As a result, the air that is supplied to the first supply air pressure chamber 403 through the air supplying pipe 417 is introduced into the first output air pressure chamber 405 through the first connecting hole 411b, to be supplied to the valve 300 through the first air outputting pipe 419. On the other hand, after the air from the valve 300 has returned to the second output air pressure chamber 406 through the second air outputting pipe 420, it enters into the discharge air duct 410c from the second opening 410b of the spool 410, to be discharged into the discharge air chamber 407.
On the other hand, when the input air pressure Pn is increased, the diaphragm 409 moves to the side of the arrow B, and, concomitantly, the spool 410 that is supported on the diaphragm 409 moves to the side of the arrow B. At this time, the spool 410, through this movement, presses the second poppet valve 414 downward against the biasing force of the second spring 416, and, as a result, the supply air valve 414b of the second poppet valve 414 opens the second connecting hole 412a. At this time, the second opening 410b of the spool 410 is closed by the discharge air valve 414a of the second poppet valve 414. On the other hand, the first poppet valve 413 is pushed upward by the biasing force of the first spring 415, and, accordingly, the supply air valve 413b of the first poppet valve 413 closes the first connecting hole 411a. At this time, the first opening 410a of the spool 410 is opened by the discharge air valve 413a of the first poppet valve 413.
As a result, the air that is supplied to the second supply air pressure chamber 404 through the air supplying pipe 417 is introduced into the second output air pressure chamber 406 through the second connecting hole 412a, to be supplied to the valve 300 through the second air outputting pipe 420. On the other hand, after the air from the valve 300 has returned to the first output air pressure chamber 405 through the first air outputting pipe 419, it enters into the discharge air duct 410c from the first opening 410a of the spool 410, to be discharged into the discharge air chamber 407.
In this way, the spool 410 and the pair of poppet valves 412 and 413 are actuated by the input air pressure Pn that is directed into the input air pressure chamber 402, where the action thereof causes the amplified output air pressures Po1 and Po2 to be outputted to the valve 300 through the air outputting pipes 419 and 420. In this case, the output air pressure Po1 can be adjusted through adjusting the pressure of the input air pressure Pn in the decreasing direction when operating the valve 300 in the forward direction, and the output air pressure Po2 can be adjusted through adjusting the pressure of the input air pressure Pn in the increasing direction when operating the valve 300 in the reverse direction.
However, with the pilot relay set forth in the aforementioned JP '718, the first output air pressure chamber 405 is adjacent to the input air pressure chamber 402, and the first output air pressure chamber 405 and the input air pressure chamber 402 are sealed together through an O-ring 422, so there is a problem in that there is a large hysteresis in the input/output characteristics.
Given this, in order to solve the problem set forth above, one may consider the use of a diaphragm instead of the O-ring 422, but because the magnitude relationships between the pressures in the input air pressure chamber 402 and the first output air pressure chamber 405 change frequently, that is, go to Po1<Pn and Po1<Pn, in what is known as pressure inversions, there would be violent changes between positive and negative pressure on the diaphragm, which would cause a reduction in the durability of the diaphragm.
Moreover, in the pilot relay disclosed in the aforementioned JP '718, a discharge air duct 410c is formed passing through the axis of the spool 410, and thus the spool 410 cannot be assembled through an easy method, such as screwing together, using a split structure, so manufacturability has been poor.
Note that Japanese Unexamined Patent Application Publication 2008-95847 (“JP '847”) discloses an example wherein the changes in pressure are violent, so that in order to suppress the inversion of pressure that acts on the diaphragm, the output air pressure chamber, the input air pressure chamber (the nozzle back pressure chamber), and the feedback chamber are not disposed so as to be mutually adjacent, where a bias chamber, a discharge air chamber, and an atmosphere chamber are disposed therebetween. However, in the structure disclosed in JP '847, at this time, the spool has only one discharge air duct that penetrates therethrough, and the spool cannot use a divided structure, and thus there is a problem remaining with manufacturability.
Moreover, in the structure set forth in JP '847, the number of chambers required within the casing is increased tremendously, requiring 11 chambers. When the number of chambers is increased, there is a problem in that there is an increase in the number of structural components, such as the number of diaphragms, as well, causing the pilot relay to become bulky and leading to problems such as increasing the size and driving up the costs of the positioners that use this technology.
The present invention was created in order to solve such problems, and the object thereof is to provide a pilot relay that is able to improve the durability of the diaphragm, and able to increase the manufacturability of the spool (the movable body) through a divided structure.